With the highly developed technology in the modern society, all kinds of sensors are conveniently used in people's daily life for a wide range of applications, from product counting and quality test in a factory to air-conditioning temperature test and TV remote control in one's house.
Among others, a photo-sensor is a very commonly used sensor, in which a photo-sensitive cell is used to convert a photo signal into an electric signal.
However, all the currently available photo-sensitive cells have a sensible wavelength range fallen around the visible region of the electromagnetic spectrum, such as the ultraviolet wavelength and the infrared wavelength; and the currently available photo sensors are not only used for measuring light intensity, but also very frequently used as a detection element for forming other types of sensors.
Infrared sensors, ultraviolet sensors, optical fiber sensors, color sensors, and CCD (charge-coupled device) image sensors are some of the currently very typical light sensors. In recent years, due to some newly emerged demands, the detection of ultraviolet light has aroused the attention of people. Advanced ultraviolet detecting instruments are required by both civil and military industries. They are used in engine control, solar ultraviolet monitoring, light source calibration, ultraviolet astronomy, flame sensor, guided-missile plume measurement, air-to-air safety communication, etc.
An ultraviolet sensor is a photoelectric device exclusively used for detecting the existence of ultraviolet light. The ultraviolet sensor is highly sensitive to ultraviolet light, particularly to the ultraviolet light produced during the combustion of wood, chemical fabrics, paper, oil, plastic, rubber, and combustible gases.
FIG. 1 is a sectional view of a conventional ultraviolet sensor 1. As shown, the ultraviolet sensor 1 includes a substrate 11, on which a first electrode layer 12, a photo-sensitive layer 13, and a second electrode layer 14 are sequentially formed. Wherein, the first electrode layer 12 is a light-pervious conducting layer, so that the photo-sensitive layer 13 is exposed to ambient ultraviolet light L. The UV-sensitive layer 13 is formed by stacking a layer of p-type semiconductor membrane and a layer of n-type semiconductor membrane.
The first electrode layer 12, the UV-sensitive layer 13, and the second electrode layer 14 of the ultraviolet sensor 1 together form a current loop. When being exposed to ultraviolet light, the UV-sensitive layer 13 releases electrons. At this point, the first electrode layer 12 is electrically connection to the second electrode layer 14 and a current is produced. By measuring an intensity of the current in the current loop, the intensity of ultraviolet light received by the ultraviolet sensor 1 can be estimated.
Generally, an ultraviolet sensor uses a UV-sensitive layer to receive ambient ultraviolet light. In the conventional ultraviolet sensor, the UV-sensitive layer is usually configured as a flat surface. This type of UV-sensitive layer having a flat surface can only respond to ultraviolet light incident on the flat surface from a particular direction, and is not able to receive incident ultraviolet light from different directions. Moreover, the flat surface of the UV-sensitive layer would reflect part of the ultraviolet light incident thereon at some incidence angles and the reflection inevitably and adversely reduces the accuracy of the ultraviolet sensor in measuring ultraviolet light.
Furthermore, most UV-sensitive layers of the conventional ultraviolet sensors are of a diode membrane structure, which have poor voltage endurance capability and accordingly, have adverse influence on the voltage endurance capability of the ultraviolet sensors and they largely shorten the usable lives of the ultraviolet sensors.